The Animal Facility Core will meet the needs of the Program Project Grant members for creating new mouse strains and for established, shared strains. To improve efficiencies the Core will provide and maintain genetically complex animals that are used by multiple projects, assist with backcrosses, and also assist with mice used in genetic mapping projects. There are four SPECIFIC AIMS for this Core. 1. To breed and genetically characterize unique and non-routine mouse strains for use by all the program project members. This service will ensure that animals are readily available for use in experiments for all of the PPG members. 2. To assist program project members with routine backcrossing of newly obtained or derived strains to the appropriate genetic backgrounds for planned studies. Fixed genetic backgrounds will be essential for many of the studies in the PPG. 3. To provide breeding and collection services for genetic mapping projects that are being performed in two of the projects in the PPG (projects 3 and 4). The Core will help with the maintenance and generation of animals in these crosses, as well as collection of DNA for genotyping. 4. To ensure animals provided to program project members are healthy and maintained in a pathogen-free environment for the proposed studies. The availability of the mouse Core will ensure that multiple investigators in the PPG will have sufficient animals available for their studies in a timely and efficient manner.